The present invention relates, in general, to a valve driving device which is used to drive the air intake and exhaust valves of internal combustion engines.
In accordance with the prior art, intake and exhaust valves for internal combustion engines have conventionally been driven by means of generally egg-shaped cams which are fixed to a cam axis and which press on the stem heads of corresponding valves by way of intermediate rocker arms. However, because there is a very small contact surface between the periphery of the egg-shaped cam and its corresponding rocker arm, rapid wearing of the surfaces occurred, causing misadjustment and warping. This not only led to difficulties with the resistance characteristics of the contacting surfaces, but also required extreme precision when manufacturing the egg-shaped cam itself.
In addition, in situations where variable timing was needed for an engine, the use of egg-shaped cams required both a low-speed cam and a high-speed cam to be mounted on the cam shaft, and further required a mechanism for switching between the two. However, the transition from a low speed to a high speed represented a change of engine specifications from that of an engine used in a general purpose automobile to those of an engine used in a racing car, and such a change was, in fact, extremely difficult to accomplish for ordinary engine operation.